The invention relates to a method for exchanging, between systems, a message which comprises at least one information element.
Such a method is generally known. During a certain transition time, one system (such as, for example, a telephone set) is based, for example, on a first (lower, old-fashioned) protocol version, and another system (such as, for example, a telephone exchange) is based, for example, on a second (higher, modern) protocol version. If all the protocol procedures of the first (lower) protocol version are incorporated in the second (higher) protocol version, a message which is based on the first (lower) protocol version and comprises an information element of a first type, is, as a result, handled in an identical manner by both systems, while a message which is based on the second (higher) protocol version and comprises an information element of a second type, in contrast is ignored by a system based on the first (lower) protocol version and is handled by a system based on the second (higher) protocol version.
This known method has the drawback, inter alia, that as a result of this method to be applied, the development of subsequent protocol versions can take place only with limited design freedom, since a message based on a lower protocol version should be handled in an identical manner by systems based on lower and higher protocol versions. Moreover, according to the known method, messages based on a higher protocol version are exchanged which have no significance whatsoever to a system based on a lower protocol version. Further, a system based on said subsequent protocol version has fewer options at its disposal than a system which would have been developed with complete design freedom, since a message to be dispatched from a system based on said subsequent protocol version to a system based on a lower protocol version should be based on the lower protocol version to permit communication between the two systems.